DC circuit breaker and method of commutation thereof

ABSTRACT

A DC circuit breaker and a method of commutation during a commutation capacitor capable of being directly charged from a main DC line are disclosed. A breaker unit is inserted in a main DC line and is connected through a first switch in parallel to a series circuit including a commutation capacitor and a reactor. At end of the commutation capacitor is connected to the power side of the main DC line, and the other end thereof to the negative bus of the DC line through a charge capacitor. A series circuit including a magnetic repulsive coil and a second switch is connected in parallel to the commutation capacitor, which is directly charged from the power side of the main DC line. When the breaker unit starts to open, the second switch is turned on so that the polarity of the charged commutation capacitor is reversed to permit a discharged current to flow in the breaker unit in the opposite direction, while at the same time starting the opening of the breaker unit.

BACKGROUND OF THE INVENTION

The present invention relates to a DC circuit breaker and a method ofcommutation thereof, or more in particular to a system for inserting areverse current by use of a commutation capacitor capable of directcharge from a DC line.

A basic circuit of a conventional DC circuit breaker of reverse currentinsertion type is shown in FIG. 1. This type of DC circuit breaker isdescribed in JP-A-No. 54-149873.

As shown in FIG. 1, a conventional DC circuit breaker of reverse currentinsertion type is configured of a breaker unit 2 inserted in series in amain DC line 1, and a series connection of a commutation capacitor 3, areactor 4 and a first switch 5 including a thyristor or a trigger gapinserted in parallel to the breaker unit 2. In FIG. 1, reference numeral1a designates a power-side terminal of the DC line 1, numeral 1b aload-side terminal of the DC line 1, numeral 6 a charge unit connectedin parallel to the commutation capacitor 3, numeral 7 a negative bus,numeral 7a a power-side terminal of the negative bus 7, and numeral 7b aload-side terminal of the negative bus 7. Further, a load 8 is connectedbetween the load-side terminals 1b and 7b. A DC power supply V isinserted between the power-side terminals 1a and 7a.

In FIG. 1, in a circuit-breaking operation, an open command is appliedto the breaker unit 2, and after the breaker unit 2 is opened, thethyristor switch 5 making up the first switch is turned on, that is,fired, so that the discharge current ○2 from the commutation capacitor 3charged in advance from the charge unit 6 is supplied in the directionreverse to the energization current ○1 of the breaker unit 2. The sum ofthe currents ○1 and ○2 flowing through the breaker unit 2 develops apoint of zero, with the result that the arc of the breaker unit 2 isextinguished, and the line current ○1 commutates to the commutationcapacitor 3, thereby completing the current-limiting process.

The above-mentioned conventional system, however, requires a charge unit6 exclusively used for charging the commutation capacitor 3. In the casewhere the capacitor is charged directly from the DC line 1, on the otherhand, the charging from the load side of the breaker unit 2 is necessarydepending on the charging polarity, and the breaking function isrequired to be given up until the capacitor 3 is completely chargedafter the breaker unit 2 is turned on, thereby hampering practicalapplications of this sytem. In the case where an exclusive charge unit 6is inserted, it is also necessary to insert an inverter for introducingpower from a DC battery or the DC line 1 to assure power reliability.This complicates the system on the one hand and reduces the reliabilityof the DC line at the same time.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a DC circuit breakerincluding a commutation capacitor capable of being directly charged froma DC line.

Another object of the present invention is to provide a DC circuitbreaker simple in construction and low in cost, in which a magneticrepulsive coil and switch means are connected in parallel to acommutation capacitor for LC resonant discharge, and by thus reversingthe charge polarity of the commutation capacitor, the charge unit iseliminated.

According to the present invention, there is provided a DC circuitbreaker comprising a commutation capacitor with an end thereof connectedto the power side of a DC line and the other end thereof to a negativebus of the DC line through a charge resistor, and a series circuitincluding a magnetic repulsive coil and a second switch connected inparallel to the commutation capacitor, in which the commutationcapacitor is charged directly from the power side of the DC line, andwhen the breaker unit starts to open, the second switch is turned onthereby to reverse the polarity of the charged commutation capacitor tosupply a reverse discharge current through the breaker unit while at thesame time starting to open the breaker unit.

The commutation capacitor is normally charged through a charge resistorfrom the DC line. When the breaker unit starts to open, the secondswitch such as a second thyristor switch is turned on, and thecommutation capacitor has the polarity thereof reversed in such a mannerthat the breaker unit is supplied with a discharge current reverse tothe energization current, while at the same time starting the opening ofthe breaker unit. Specifically, when the second thyristor switch isturned on, the commutation capacitor is discharged by resonance throughthe magnetic repulsive coil and the second thyristor switch. When aresonance current flows in the magnetic repulsive coil, a magneticrepulsion force is generated thereby to start to open the breaker unit.The resonance current is blocked by the second thyristor switch at thezero current point in the half cycle, in which case the charge polarityof the commutation capacitor is reversed. In this way, when the firstswitch such as the first thyristor switch is turned on at the time ofopening the breaker unit, a discharge current reverse in direction tothe energization current flows from the commutation capacitor through areactor to the breaker unit, thus breaking the line current. A DCcircuit breaker comprising a commutation capacitor capable of beingdirectly charged from a DC line is thus provided in which thesatisfactory functions thereof are not adversely affected even when thecommutation capacitor is charged directly from the DC line.

BRIEF DESCRIPTION 0F THE DRAWINGS

FIG. 1 is a diagram showing a basic circuit of a conventional DC circuitbreaker of reverse current insertion type.

FIG. 2 is a diagram showing a circuit of a DC circuit breaker ofreverse/current insertion type according to the present invention.

FIGS. 3 and 4 show other practical embodiments of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A circuit diagram of a DC circuit breaker of reverse current insertiontype according to an embodiment of the present invention is shown inFIG. 2.

Those component parts identical to the parts in FIG. 1 are designated bythe same reference numerals and are not described. In this embodiment, acommutation capacitor 3 has an end thereof connected to the powersideterminal 1a of a DC line 1 and the other end thereof connected through acharge resistor 9 and a diode 10 to a negative bus 7 of the DC line 1.At the same time, the commutation capacitor 3 is connected in parallelto a series circuit including a magnetic repulsive coil 11 and a secondthyristor switch 12 making up a second switch.

Now, explanation will be made of the commutation processes of the DCcircuit breaker according to the present invention with reference toFIG. 2.

(i) The commutation capacitor 3 is normally charged directly from the DCpower supply V side of the DC line 1 through the charge resistor 9 andthe diode 10 as shown by +. (charge current ○3 )

(ii) Then, the second thyristor switch 12 is turned on, with the resultthat the commutation capacitor 3 is discharged by LC resonance throughthe magnetic repulsive coil 11 and the second thyristor switch 12. Whenthe LC resonance current ○4 flows in the magnetic repulsive coil 11, amagnetic repulsive force is generated thereby to start the opening ofthe breaker unit 2. The LC resonance current ○4 is blocked by the secondthyristor switch 12 at the point of zero current in the half cycle, inwhich case the charge polarity of the commutation capacitor 3 isreversed as shown by (+).

(iii) When the first thyristor switch 5 is turned on with the opening ofthe circuit breaker unit 2, a discharge current ○5 reverse in directionto the energization current ○1 flows in the breaker unit 2 from thecommutation capacitor 3 through the reactor 4 and the first thyristorswitch 5, so that the current flowing in the breaker unit 2 develops azero current point, with the result that the arc of the breaker unit 2is extinguished.

(iv) When the arc of the breaker unit 2 is completely extinguished andthe circuit is thus broken, the commutation current ○6 flows through theDC power supply V, the commutation capacitor 3, the reactor 4, the firstthyristor switch 5, the load 8 and the negative bus 7 in that order.

A DC circuit breaker having a commutation capacitor 3 capable of beingcharged directly from the DC line 1 is thus provided, which displays thefunctions thereof in satisfactory manner even when the commutationcapacitor 3 is charged directly from the DC line 1 through the processdescribed above.

Specifically, according to the present invention, a series circuitincluding the magnetic repulsive coil 11 and the second thyristor switch12 is connected in parallel to the commutation capacitor 3, and thecommutation capacitor 3 is connected through the charge resistor 9 andthe diode 10 to the negative bus 7 and the power side of the line 1. Bydoing so, the commutation capacitor 3 is charged positively on the leftside in FIG. 2 from the DC line 1 through the charge resistor 9 and thediode 10 in a manner irrespective of the open or closed condition of thebreaker unit 2. Upon issue of a break command for the breaker unit 2,the second thyristor switch 12 is turned on, and the commutationcapacitor 3 is discharged by resonance through the magnetic repulsivecoil 11 and the second thyristor switch 12. When the LC resonancecurrent ○4 flows in the magnetic repulsive coil 11, a magnetic repulsiveforce is generated thereby to start the opening of the breaker unit 2.This LC resonance current ○4 is blocked by the second thyristor switch12 at the zero current point in the half cycle, and the charge polarityof the commutation capacitor 3 is reversed with the right side thereofto positive in the drawing. When the breaker unit 2 has fully opened,the first thyristor switch 5 is turned on, so that the commutationcapacitor 3 is discharged by resonance through the reactor 4, the firstthyristor switch 5 and the breaker unit 2. As a result, the breaker unit2 is supplied with a current ○5 reverse in direction to the line current○1 that is an energization current and thus develops a zero currentpoint. The breaker unit 2 is therefore extinguished, and the linecurrent ○1 commutates to the commutation capacitor 3 thereby to completethe current limiting process.

Generally, the output of the magnetic repulsive coil 11 used as aresonance circuit for reversing the charge polarity of the commutationcapacitor 3 has such a characteristic as to decrease sharply with theincrease in the clearance from the conductive short ring opposedthereto, and most of the effective output of the magnetic repulsive coil11 is generated in the half cycle of the resonance current thereof.Therefore, the output is not substantially reduced if the resonancecurrent of the magnetic repulsive coil 11 is blocked in half cycle. Bythus blocking the current in half cycle, it is thus possible to utilizeas a commutation energy the energy which otherwise would be consumed bythe resistance of the subsequent circuit portions, thereby making itpossible to reduce the whole charging energy for the commutationcapacitor.

A circuit of a second embodiment of the present invention is shown inFIG. 3, in which the reactor 4 of FIG. 2 is arranged at a differentpoint. Specifically, in FIG. 3, the reactor 4 may be located at any ofthe points 4a or 4b with quite the same effect as in the firstembodiment shown in FIG. 2.

Further, the reactor 4 may be done without if the reactance L of thewire is used.

A circuit according to a third embodiment of the present invention isshown in FIG. 4. In this embodiment, a trigger gap is used in place ofthe thyristors making up the first and second switches in FIG. 2 withexactly the same effect as in the first embodiment of FIG. 2.

According to the present embodiment, as explained above, the commutationcapacitor 3 is capable of being charged directly from the power side ofthe DC line 1, and therefore a predetermined charge voltage and polarityare obtained in a manner irrespective of the open or closed condition ofthe breaker unit 2, thus eliminating the need of an exclusive chargeunit. The reliability of the DC line 1 is thus improved while at thesame time providing an economical DC breaker unit. Further, effectiveutilization of the charging energy of the commutation capacitor 3 ismade possible, thus reducing the capacitance of the commutationcapacitor 3.

The breaker unit 2 may take the form of vacuum circuit breaker, gascircuit breaker or air circuit breaker, of which the vacuum circuitbreaker is considered as the best choice as a circuit breaker unit 2 inview of the fact that it has a superior high-frequency current breakingperformance, that the resonance discharge current of the commutationcircuit configured of the commutation capacitor 3 and the reactor 4 maybe supplied in high frequency to reduce the capacitance of thecommutation capacitor 3, and that a small opening stroke provides asufficient extinguishing ability for suitable application to high-speedbreaking.

Further, instead of the magnetic repulsive coil 11 explained above as aresonance discharge circuit for reversing the charge polarity of thecommutation capacitor 3, any coil for driving the breaker unit 2 to openside may be used with equal effect.

It will thus be understood from the foregoing description that accordingto the present invention, a commutation capacitor is capable of beingcharged directly from the DC line, thereby making possible a DC breakerunit having such a commutation capacitor.

Furthermore, according to the present invention, there is provided a DCcircuit breaker low in cost and simple in construction eliminating theneed of a charge unit by inserting a magnetic repulsive coil and switchmeans in parallel to a commutation capacitor and reversing the chargepolarity of the commutation capacitor.

We claim:
 1. A DC circuit breaker comprising:a breaker unit arranged ina main DC line; a first series circuit including a commutationcapacitor, a reactor and first switch means inserted in parallel to thebreaker unit; a charge resistor inserted between the negative bus of theDC line and the commutation capacitor; and a second series circuitincluding a magnetic repulsive coil and second switch means arranged inparallel to the commutation capacitor, wherein a reverse current issupplied to the DC line by LC resonance thereby to generate a zerocurrent and to extinguish an arc in the breaker unit.
 2. A DC circuitbreaker comprising:a breaker unit arraned in a main DC line; a firstseries circuit including a commutation capacitor, a reactor and a firstthyristor inserted in parallel to the breaker unit; a charge resistorinserted between the negative bus of the DC line and the commutationcapacitor; and a second series circuit including a magnetic repulsivecoil and a second thyristor arranged in parallel to the commutationcapacitor, wherein a reverse current is supplied to the DC line by LCresonance thereby to generate a zero current and to extinguish an arc inthe breaker unit.
 3. A DC circuit breater comprising:a breaker unitarranged in a main DC line; a first series circuit including acommutation capacitor, a reactor and a first trigger gap inserted inparallel to the breaker unit; a charge capacitor inserted between thenegative bus of the Dc line and the commutation capacitor; and a secondseries circuit including a magnetic repulsive coil and a second triggergap arranged in parallel to the commutation capacitor, wherein a reversecircuit is supplied to the DC line by LC resonance thereby to generate azero current and to extinguish an arc in the breaker unit.
 4. A DCcircuit breaker comprising:a vacuum interruption arranged in a main DCline; a first series circuit including a commutation capacitor, areactor and first switch means inserted in parallel to the vacuuminterruptor; a charge resistor inserted between the negative bus of theDC line and the commutation capacitor; and a second series circuitincluding a magnetic repulsive coil and second switch means arranged inparallel to the commutation capacitor; wherein a reverse current issupplied to the DC line by LC resonance thereby to generate a zerocurrent and to extinguish an arc in the vacuum interruptor.
 5. In a DCcircuit breaker comprising a breaker unit arranged in a main DC line afirst series circuit including a commutation capacitor, a reactor andfirst switch means inserted in parallel to the breaker unit, a chargeresistor inserted between the negative bus of the DC line and thecommutation capacitor, and a second series circuit including a magneticrepulsive coil and second switch means arranged in parallel to thecommutation capacitor,a method of commutation of the DC circuit breakercomprising the steps of (1) charging the commutation capacitor normallythrough the charge resistor directly from the DC power side of the mainDC line, (2) turning on the second switch means, discharging thecommutation capacitor by LC resonance through the magnetic repulsivecoil and the second switch means, and thus reversing the chargingpolarity of the commutation capacitor, and (3) turning on the firstswitch means when the breaker unit starts to open, thereby supplying thebreaker unit, from the commutation capacitor through the reactor and thefirst switch meqans, with a discharge current reverse in direction tothe energization current flowing in the main DC line thereby to generatea zero current and to extinguish an arc in the breaker unit.